Easily openable tightly sealed bag

ABSTRACT

This invention provides an easily openable tightly sealed plastic bag which is formed of a film containing at least a substrate layer and a heat seal layer and is possessed of a sealed part whose substrate layer contains a multiplicity of through cuts, these cuts being formed substantially on the edge lines and partly or wholly closed with the heat seal layer. This tightly sealed bag safely retains the practical strength normally expected of any bag and avoids accidentally sustaining rupture while the bag is being transported or handled and yet permits itself to be opened with the force of finger tips. This invention manifests its utility particularly in a tightly sealed bag which is formed of a substrate of high strength and high barrier property. This invention further provides a method suitable for the production of the tightly sealed bag described above and a device to be used in working the method. The easily openable tightly sealed plastic bag of particularly desirable quality can be obtained by the method and the device so provided by this invention.

This application is a continuation of application Ser. No. 803,446 filedDec. 2, 1985.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

This invention relates to an easily openable tightly sealed plastic bagso fabricated that it can safely retain the practical strength normallyexpected of any bag, avoid accidentally sustaining rupture while the bagis being transported or handled, and be opened with the force of fingertips, to a method for the production thereof, and to a tool to be usedin working the method.

2. Description of the Prior Art:

Plastic films and laminated films made of superposed layers of plastics,aluminum foil or other metals, paper, and other materials are light inweight, excel in airtightness, and possess high strength and ease ofhandling. Bags made of such films can be tightly sealed simply byheat-sealing without particularly requiring use of any adhesive agent.Owing to these merits, the films have been recently used extensively toproduce tightly sealed bags for various commodities such as foodstuffs,pharmaceutical products, and sundries which come in various forms suchas liquid, powder, paste, and solid.

In such a tightly sealed bag as described above, the strong point ownedby the material of the bag ironically offers resistance to tearing andrenders the bag hardly openable. Generally, the film for use in thetightly sealed bag is tough but, once a cut is inflicted in the bag, isliable to propagate the cut. When one point somewhere in the edge of thebag is cut in advance, therefore, the bag can be opened by the force offinger tips applied so as to widen the cut.

The method of forming an I notch of not less than 2 mm in length in thetransverse direction in advance somewhere in the heat-sealed edge of abag of such a film has been already employed. This method, however, hasa disadvantage that the notch so formed in the edge of the bag can notbe found readily. The method of forming a V notch somewhere in the edgeof a bag of such a film is also used. In accordance with this method, itis somewhat easy to find the notch formed in the bag. When this methodis employed where a large number of bags are produced and packed, thereis a possibility that V-shaped film scraps resulting from the insertionof V notches will scatter, adhere to the packed products, anddeteriorate the factory environment. U.S. Pat. No. 3,650,461 disclosesan invention which forms a circular through hole in a sealed portion ofa bag. This method also gives rise to a circular scrap and entails aproblem similar to the problem suffered by the aforementioned method ofinserting a V notch. Moreover, the bag bearing the circular through holehas a problem that desired tearing of the bag necessitates considerablylarge force because of the force of finger tips applied in an effort tostart a tear in the bag results in concentration of stress around theboundary of the circular through hole and consequent elongation of thebag around the circular through hole.

In any of the methods described above, since the point for starting atear in the bag is formed at a specific location, it does not alwaysturn out to be an advantageous location. There is a possibility that atear will propagate in an unexpected direction and induce unexpectedspilling of the contents. In the case of the method of inserting an Inotch or a V notch, since the notch is generally large (at least 2 mm inlength), the notch inserted in the film before its fabrication into abag renders the film readily tearable and even prevents the film frombeing effectively fabricated into a bag.

Japanese Utility Model Publication No. 22,484/1979 discloses a bag ofplastic film having, as points for starting a tear in the bag, aplurality of small punched holes, small embossed holes, or small slitsof successively decreasing sizes arranged inwardly from the edge of thebag in at least one of the sealed sides of the bag. Of the bags proposedby this Publication No. 22,484/1979, those provided with small punchedholes and small slits have a disadvantage that once tears start in thesebags, they rapidly propagage along the rows of holes or slits which areprovided to start a tear, and the tears so growing induce fracture ofbags to spill their contents while the bags are being transported orhandled. The bag provided with embossed holes have a disadvantage thatsince the holes are merely depressed and are not perforated, they do noteasily start tears in the bag unless they are exposed to fairly greatforce.

Japanese patent application Laid-open No. 160251/1983 discloses atightly sealed dispensing bag possessing at least three heat-sealededges and having a multiplicity of scratches closely formed in edgeportions of the bag substantially perpendicularly to the edges. Thescratches in this bag are formed as by rubbing with a grindstone and thelike. This dispensing bag, therefore, has a disadvantage that thescratched surface caused by the rubbing is conspicuous and impairs itsexternal appearance. There is also a possibility that the scratches areliable to be irregular and uneven in size and direction, causing the bagto be opened with difficulty, and the direction of tearing is notuniform.

Besides the various problems described above, the conventional bags havea disadvantage that they are openable only partially depending on howthe bags are formed. For example, in the case of the so-called pillowtype bag having a notch and a sealed portion formed in the longitudinaldirection at the center and the sealed portion produced by overlappingand heat-sealing the opposed ends of the film without allowing theheat-sealed ends to protrude from the boundary of the bag as illustratedin FIG. 20 and FIG. 21, a tear started from the notch 7 ceases topropagate after reaching the heat-sealed portion, leaving the bag onlyhalf opened. In this case, it causes inconvenience that the content ofthe bag has to be drawn out through the small opening barely formed asdescribed above. Where the content is in a solid shape, it isparticularly hard to pull out of the bag. It also causes a disadvantagethat since the bag is hardly opened it is quite difficult to take outits contents when the width of the contents such as of a medically usedarticles is very close to that of the bag.

SUMMARY OF THE INVENTION

This invention has been established with a view to overcoming thedrawbacks suffered by the conventional plastic bags. It is aimed atproviding a tightly sealed bag containing ideal cuts or small slits.This bag is free from forming any cut scraps of the film in the courseof its production, allows no mingling of foreign matters into itsinterior, and retains the practical strength. And it can be torn withthe force of finger tips at any desired position in the edge portions toopen the bag enough to permit easy removal of the contents. Theinvention provides also a method for the production of the tightlysealed bag, and a tool to be used in working the method for productionof the bag.

To be specific, this invention in its first aspect concerns an easilyopenable tightly sealed plastic bag formed of a film containing at leasta substrate layer and a heat seal layer and possessed of a sealed part,which bag is characterized by the sealed part containing in thesubstrate layer of multiplicity of through cuts and the through cutsbeing substantially formed in the edge portion of the bag and partly orwholly closed with the heat seal layer.

This invention in its second aspect concerns a method for the productionof an easily openable tightly sealed plastic bag, characterized byforming a multiplicity of through cuts in a film containing at least asubstrate layer and a heat seal layer, then folding the film therebyenabling the edge portions containing said through cuts to constitutepartly or wholly the sealed edge portions of a bag, and heat-sealing thesuperposed edges or inner sides thereof thereby completing a tightlysealed bag having at least three edges thereof heat-sealed.

This invention in its third aspect concerns a method for the productionof an easily openable tightly sealed bag, characterized by forming amultiplicity of through cuts in a substrate film, binding a heat sealfilm on one side of the substrate film, then folding the bound filmsthereby enabling the bordering portions containing said through cuts toconstitute partly or wholly the sealed edge portions of a bag, andheat-sealing the superposed edges or inner sides thereof therebycompleting a tightly sealed bag.

This invention in its fourth aspect concerns a slit imparting toolhaving blades of fine protrusions linearly aggregated thereon, whichtool is characterized by said fine protrusions individually possessing aridge and said ridge partly or wholly constituting a cutting edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view illustrating a section of the through slits formedin a film prior to heat-sealing with the tool shown in FIG. 11[corresponding to a view taken on line X--X of FIG. 3(b)]. FIG. 2(a) and(b) are cross-sections illustrating the heat-sealed portion of foldedfilms. FIG. 2(c) is an enlarged view of the portion of the film withincircle (c) in FIG. 2(a) and illustrates a through cut partially filledby the heat seal layer material. FIG. 2(d) is an enlarged view of theportion of the film within circle (d) in FIG. 2(a) and illustrates athrough cut wholly filled by the heat seal layer material.

FIG. 3(a), (c), and (d) are plan views illustrating one end face of afilm, (a) showing a state prior to sealing and, (c) a state aftersealing, (d) a state after sealing with the through slits arrangeddifferently, is and

FIG. 3(b) an enlarged view of the through slit encircled with a dash anddotted line in (a).

FIG. 4 and

FIG. 5 are explanatory diagrams on the mechanism of tearing.

FIG. 6 and

FIG. 7 are perspective views of tightly sealed bags.

FIG. 8 is a plan view of a film processed for fabrication of bags.

FIG. 9 is a perspective view of a tightly sealed bag.

FIG. 10 is an enlarged transverse perspective view illustrating thetightly sealed bag of FIG. 9.

FIG. 11 is a diagram illustrating protrusions on a tool in a magnifiedstate.

FIG. 12 is a cross section illustrating a typical process for theproduction of such a protrusion.

FIG. 13 is a perspective view of a fabricating wheel.

FIG. 14 is an enlarged plan view of part of the circumferential surfaceof the wheel of FIG. 13.

FIG. 15 is an explanatory diagram illustrating a typical fabricationperformed on a film.

FIG. 16 is a perspective view illustrating another typical process forthe production of a tool as another embodiment of the present invention.

FIG. 17 is a perspective view of protrusions.

FIG. 18 is a perspective view illustrating a tool having protrusionsformed on a flat bar.

FIG. 19 is a perspective view illustrating a tool having protrusionsformed on a plate cut out of a disk.

FIG. 20 is a perspective view illustrating one example of theconventional tightly sealed bags.

FIG. 21 is an enlarged transverse perspective view illustrating thesealed bag of FIG. 20.

FIG. 22 is a micrograph showing a section of a cut in the sealed portionof the tightly sealed bag of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The substrate layer in the film of which the tightly sealed bag of thisinvention is produced is formed of a material required to withstand theheat used for heat sealing of the portions of the film for forming asealed part and possesses strength enough to withstand impacts normallyexerted during the course of fabrication such as printing, laminating,packing, transportation, and storage. Examples of the materialfulfilling the requirement include polyamide (nylon), polyester,biaxially oriented polypropylene, cellophane, cellulose acetate, andrigid PVC resin. The substrate layer of such a material is so tough thatit is hard to start a tear in the film with the force of finger tips.Generally, prior to its use in the production of a bag, the substratelayer of this nature has a heat sealable plastic film, i.e. a heat seallayer, superposed fast thereon. This heat seal layer is formed of amaterial which is fusible with the heat to be used during the heatsealing of the opposed portions of the film for the formation of asealed part. Examples of the material fulfilling the requirement includesuch olefin type resins as low-density polyethylene (high-pressurepolyethylene and low-pressure straight-chain low-density polyethylene)and nonstretched polypropylene and polyethylene-vinyl acetate copolymer.Although the temperature for the heat sealing is variable with variousfactors such as the magnitude of pressure applied, the duration ofpressure application, and the thickness and kind of the film used, it isgenerally selected in the range of 80° to 180° C., preferably 120° to150° C. The material of the heat seal layer is desired to assume acompletely molten state or at least a half-molten state at thetemperature of the heat sealing described above. The heat seal layer maybe formed of a single material which is capable of being heat-sealed asdescribed above. It may be further provided with a layer of anchor coatagent to increase bond strength. Many isocyanate type anchor coat agentsexhibit excellent properties.

The heat seal layer is desired to possess a smaller tensile strengththan the substrate layer, and it is also desired to possess a greatertear strength than the substrate layer. The tear strength is determinedaccording to the method of JIS P 8116 on a test sample which is notched.

Specifically, the materials for the substrate layer and the heat seallayer are desired to be selected so that the tensile strength of theheat seal layer material will be not more than 2/3 and not less than1/20 of the tensile strength of the substrate layer material, and thatthe tear strength (JIS P 8116) of the heat seal layer material will benot less than 5 times and not more than 150 times that of the substratelayer material. Examples of determining the commercially availableplastic films are shown below.

                  TABLE                                                           ______________________________________                                                         Item                                                                          Tensile                                                                       strength Tear strength                                                        MD/TD    MD/TD                                                                Test method                                                                   JIS Z 1707                                                                             JIS P 8116                                                           Unit                                                                                Kg/15 mm   Kg/15 mm                                    Material    Thickness  in width   in width                                    ______________________________________                                        Biaxially stretched                                                                       15 μm   2.8/2.8    15/15                                       nylon film                                                                    Polyvinylidene                                                                            17 μm   2.8/2.8    15/15                                       chloride-                                                                     coated biaxially                                                              stretched                                                                     6-nylon film                                                                  Biaxially stretched                                                                       12 μm   2.1/1.9     5/10                                       polyester film                                                                Biaxially oriented                                                                        20 μm   3.3/7.2    15/10                                       polypropylene film                                                            Cellophane  22 μm   3.5/1.9    10/10                                       Polyvinyl chloride                                                                        30 μm   2.5/2.7    30/60                                       film                                                                          Low-density 30 μm   0.6/0.4    200/500                                     polyethylene film                                                             Linear low-density                                                                        50 μm   1.8/1.4    400/900                                     polyethylene film                                                             ______________________________________                                    

The materials for the substrate layer and the heat seal layer selecteddescribed above are desired to be processed so that the thickness ratioof the substrate layer to the heat seal layer falls in the range of 5:1to 1:10, it is more preferable when the substrate layer is 10 to 50 μm,the heat seal layer 10 to 100 μm, and the total film 20 to 150 μm, inthickness, so that the produced bag possesses an easy openability and aresistance to breakage in harmony. Namely, tearing is easily donestarting from the through cuts formed in the substrate and an unexpectedtearing and quick propagation can be curbed. Thus, a possible breakagein the bag during transportation and handling can be prevented.

When a film made of such a resin as polyester resin or polyamide resinwhich has a barrier property, strength, and heat-resisting property or alaminated film containing at least one layer of the aforementioned filmis used as the substrate layer, a tightly sealed bag obtained issuitable for the production of packages of high quality. A film obtainedby laminating an aluminum foil and a plastic layer or a film having athin metal containing such as of aluminum deposited on a plastic film byvacuum deposition, sputtering, or ion plating is useful as a substratelayer excelling in barrier property. Further, a laminated film obtainedby superposing a barrier layer such as of vinylidene chloride type resinon a plastic layer such as of polyester, polyamide, or polypropylenealso constitutes itself a desirable substrate layer for the film of thisinvention.

For example, a laminated film is desired to be consisting of paper /PE₁/AC/PET/PE₂ (PET denotes a polyethylene terephthalate substrate layer,AC an anchor coat layer, PE₂ a polyethylene heat seal layer, and PE₁ apolyethylene adhesive layer), where the paper layer is superposed to beplaced on the surface opposite from the heat seal layer, or consistingof PET/PE₁ /paper/PE₂, so that the through slits are concealed withpaper or become inconspicuous. Thus, the film comes to have a favorableappearance. The present invention forms a multiplicity of through slitssubstantially in the edges. The expression "substantially in the edges"denotes that the through slits may be formed in a slightly inner portionfrom and along the edges or in the edges.

The through cuts or slits may be formed in zigzag pattern as illustratedin FIG. 3(c) or in series as illustrated in FIG. 3(d).

The through cuts or slits according to this invention do not denotecompletely opened through holes but denote the cuts left in thesubstrate layer after being formed through the substrate layer withoutproducing the substrate layer scraps as shown in FIG. 2(a) and (b).

In the present invention, the through cuts or slits formed in thesubstrate layer are to be partly or wholly closed with the heat seallayer. The term "closed" denotes that:

(1) the heat seal layer material is filled into the through slits,

(2) the heat seal layer material penetrates into the through slits butdoes not fully fill them. The heat seal layer is heat-sealed around thethrough slits and closes their openings, and

(3) the heat seal layer does not penetrate into the through slits but isfused around them to cover and close their openings.

The expression "wholly closed with the heat seal layer" means that allthe numbers of slits are closed with the heat seal layer in one or atleast two ways of the above (1), (2), and (3).

The expression "partly closed with the heat seal layer" means that:

A. Some numbers of the whole slits are closed with the heat seal layerin one ar at least two ways of the above (1), (2), and (3), and

B. The heat seal layer material penetrates partly into the openings ofthe slits, or the openings are partly covered with the heat seal layerto narrow the opening area of the slits. But, the slits are not closedas in the above three ways (1), (2), and (3).

The through slits formed without producing film scraps by the presentinvention are in a slender shape having a length not exceeding 0.5 mm,preferably not exceeding 0.3 mm and exceeding 0.1 mm. As illustrated inFIG. 3, the through cuts 1 are disposed in a film 8 in a transversaldirection relative to an edge line 2. Cracks (not illustrated in thedrawing) start from the terminals 3, 4 of each through cut 1 shown inFIG. 4. Virtually no crack is seen to occur at any other point of thethrough cut. When a group of such through cuts is located substantiallyon the edge line, tears in the bag start from the inner terminals 4 ofthe through cuts 1. When such through cuts are located as separatedinwards from the edge line 2, the stress exerted as indicated by thearrows in FIG. 4 causes tears to start from the edge line side terminals3 of the through cuts toward the edge line 2 as indicated by the arrowof dotted line in FIG. 4. After the tears have reached the edge line,the tears begin to propagate in the transversal direction from the otherterminals 4 of the through cuts as illustrated in FIG. 5.

The slender through cuts 1 substantially perpendicular to the edge line2 are disposed ideally at 90° relative to the edge line. In actuality,the through cuts advantageously fulfil their part of this invention solong as they are disposed at angles falling in the range of 70° to 110°,preferably 75° to 105°.

The through cuts formed without producing film scraps means localinjuries produced in the film as by causing the relevant portions of thefilm to be pulled outwardly or by inserting partial cuts in theportions, so that during the infliction of such injuries, absolutely nopart is cut out from the film. The through cuts are formed in suchportions of the film that are destined to form an edge portion when theopposed ends of the film are heat-sealed to complete a bag. When thefilm is thick and tough, these through cuts are required to be formed soas to border on the edge line. When the film is thin, they are desiredto be located at a distance of 0.5 to 3 mm inwardly from the edge line.

In accordance with this invention, when the film having the through cuts1 formed in advance is folded and the opposed ends of the folded filmare heat-sealed to form a sealed part of a bag as illustrated in FIG. 1,the molten heat seal layer 17 is allowed to enter the through cutsformed in the substrate layer 16 and substantially fill up the throughcuts as illustrated in FIG. 2(a(d). In FIG. 2(a) and (b), 18 representsa through cut filled by the heat seal layer material. A through cutpartially filled by the heat seal layer material is shown in FIG. 2(c)and a through cut wholly filled by the heat seal layer material is shownin FIG. 2(d). Since the through cuts are filled up in their fairly largeportions, a possible decrease in the strength of the tightly sealed bagdue to the presence of such through cuts can be represented to theminimum.

In the sealed part of the tightly sealed bag of this invention, the cutsmay be distributed, so that those formed in one of the sealed substratelayers of film deviate from those formed in the other substrate layer asillustrated in FIG. 2(a) or they coincide with those formed in the othersubstrate layer as illustrated in FIG. 2(b). Where the material for thesubstrate layer of the film possesses notably high tear strength, thedisposition of the through cuts in their mutually coinciding positionsproves more desirable from the standpoint of easy opening of the bag.When the through cuts formed in one of the substrate layers coincidewith those formed in the other substrate layer, easy openability of thebag is sufficiently attained even if the pitch l between the cuts isdistant as shown in FIG. 3(c), (d). For example, the pitch l may beenlarged to about 5 mm. When the through cuts formed in one of thesubstrate layers do not coincide with those formed in the othersubstrate layer, it is preferably to fix the pitch l at not more than1.5 mm, preferably in the range of about 1.0 to 1.5 mm from thestandpoint of the easy opening property. The through cuts may be formedin a single row or in a plurality of rows of at least two. Where thethrough cuts are formed in a plurality of rows, the width of a group ofcuts is desired to be not more than 5 mm, preferably not more than 3.5mm.

As concerns the pattern of the tightly sealed bag produced by thisinvention, the bag may be sealed on three of the four sides asillustrated in FIG. 6 or sealed on all the four sides as illustrated inFIG. 7. In the diagrams, 5 stands for a heat-sealed portion in thelongitudinal direction and 6 for a heat-sealed portion in the lateraldirection. When the heat sealed portions 5 are formed on the outermostedges, the cuts are to be disposed in the outskirts of the sealedportions. FIG. 6 depicts a group of through cuts 1 formed on the edgelines and FIG. 7 a group of cuts 1 formed at a distance inwards from theedge lines. When part of the opposed ends of the folded film remainunsealed outside the sealed portion of the completed bag, the group ofcuts is to be similarly formed in the edge portion of the unsealed partof the opposed ends of the folded film. In the film of this invention,the groups of through cuts are located locally or throughout the entirelengths of the opposite edge portions of the film in its unfolded state.When this invention is embodied in a mass-production system using anautomatic bag-making and bag-filling machine adapted to cut a film inthe longitudinal direction and, at the same time, produce at least twobags at a time, groups of through cuts are to be disposed each inseveral rows in the longitudinal direction. Where groups of through cuts1 are disposed longitudinally and laterally after the pattern of acheckerboard as shown in FIG. 8, there can be obtained bags which aresealed on all the four sides and, therefore, are openable in any of thefour directions.

A bag having three sealed portions as illustrated in FIG. 9 can be alsoproduced. FIG. 10 is a perspective view illustrating the bag of FIG. 9in an enlarged transversally sectioned state. In this case, the oppositeends of the film 8 to be heat-sealed with each other are overlapped andthen heat-sealed in the overlapping state. Thus, the heat-sealed portiondoes not protrude from the boundary of the bag surface. When the groupof through cuts contemplated by this invention is formed in the outskirtof the longitudinally heat-sealed portion 5, the tear propagated is notstopped in the longitudinally fused portion but allowed to cross theentire width of the bag. Therefore, the contents in the shape of rigidbar or having a broad width close to that of the bag can be easily takenout of the bag.

The group of through cuts contemplated by this invention can be disposedthroughout the entire length of the edge line. Optionally, they may beformed intermittently or locally as illustrated in FIG. 9.

The tool to be used for forming such through cuts as described above isnot specifically limited. A metallic roll having a multiplicity ofslender cutting edges formed on the circumferential surface thereof or ametallic plate having the same cutting edges formed on the flat surfacethereof can be advantageously used. For example, by makingpseudotriangular cuts 21 in a metallic surface 9 and causing metallicportions separated from the metallic surface by the cuts to be raisedrelative to the bases of the pseudotriangles as axes as illustrated inFIG. 12, protrusions 10 are created and cut portions remain asdepressions 11. The angle which the depression side surfaces of theprotrusions 10, namely the bluff surfaces 12, form relative to themetallic surface is desired to exceed 60° and not to exceed 90°. Themetallic material on which such protrusions as mentioned above have beenarranged in at least one straight row is hardened and used as the tool.FIG. 13 is a perspective view of a processing roll 13 having suchprotrusions formed on the circumferential surface thereof and FIG. 14 isa plan view illustrating the portion of the processing roll 13 of FIG.13 enclosed with a dash and dotted line in an enlarged state.

When the protrusions 10 illustrated in FIG. 11 are pressed against afilm, the curved edges of the bluff surfaces 12 function as cuttingedges, so that the edges of the bluff surfaces 12 will be straightlyinserted into the portions of the film falling under the bluff surfaces12 side and the outer sloped surfaces 19 will expand the portions of thefilm by the pressure exerted. As a result, the portions of the filmwhich have admitted the insertion of the bluff surfaces 12 remain flatand the portions which have admitted the outer sloped surfaces 19 aredeformed aslant downwardly and strained and come to differ from thelevel of the remaining portions of the film as illustrated in FIG. 1.The film is provided with the strained portions and the undeformedportions with the cuts therebetween. When the film is heat-sealed, thestrained portions of the film are almost returned to their originalstate to coincide with the level of the remaining portions of the film,but they still possess the internal strain remained therein and, becauseof the internal strain, the strength of the film is lowered.Consequently, an important effect that the film is readily torn with theforce of fingers from the bordering portion between the strained portionand the unstrained portion. Unlike the injuries inflicted by insertionof conventional cutting edges, cracks run from the opposite terminals ofthe through cuts produced as described above. These cracks are highlyeffective in starting tears in the film. When the through cuts shown inFIG. 1 and formed with the tool illustrated in FIG. 11 are heat-sealed,the portions deformed aslant downwardly are restored substantially toits original flat state as illustrated in FIG. 2(a), (b).

FIG. 15 is an explanatory diagram illustrating a typical setup forworking on a film by the use of the processing roll illustrated in FIG.13. The processing roll 13 and a retainer roll 14 are held in mutualcontact and are rotated in opposite directions at one equal peripheralspeed. The film 8 is passed through the two rolls. During the course ofthis passage, the film 8 is depressed by the protrusions 10 on theprocessing roll 13, with the result that through cuts 1 are disposed inthe film in the pattern as illustrated in FIG. 3. In the diagram, 15stands for a roll of film.

In order to form the through cuts in the film, the tool may be used inthe shape having protrusions 10 created on the surface of a flat bar asillustrated in FIG. 18 or in the shape having protrusions 10 created ona semicircular plate cut out from a disk as illustrated in FIG. 19.

The tool used in the present invention is desired to be made of a rigidmaterial including a hardened steel and ceramics such as siliconcarbide, titanium carbide, and silicon nitride. Where the tool shapedfrom a metallic material is covered with a thin coat of silicon carbideor titanium carbide, the obtained tool also exhibits outstandingwear-resistance and provides a sharp cutting for a long time.

Now, the methods available for the production of the easily openabletightly sealed bag of this invention will be described below.

These methods are roughly classified into the following two types: (1)The method which comprises inflicting through cuts in a film which hasthe substrate layer and the heat seal layer joined in advance bylamination and (2) the method which comprises first inflicting throughcuts in the substrate layer and subsequently superposing the heat seallayer fast on one of the surfaces of the substrate layer. The procedurewhich follows the infliction of the through cuts, namely the procedurewhich comprises folding the film in such a manner that the portionsbearing the aforementioned through cuts will be opposed to each other toform a portion or the entire portion of the sealed edge portions of abag and heat-sealing the opposed edge portions or the inner sidesthereof thereby giving rise to a tightly sealed bag, is applicablecommonly to the two major methods (1), (2) mentioned above.

When the easily openable tightly sealed bag is produced by inflictingthrough cuts in the film by the above method (1), folding the film insuch a manner that the portions bearing such through cuts will besuperposed to form a portion or the entire portion of the sealed edgeportions of a bag and heat-sealing the opposed edge portions therebyforming a sealed part in the completed bag, the through cuts are partlyor wholly blocked with a heat seal layer as illustrated in FIG. 2(a) and(b) and they are distributed only in the heat-sealed portions. When theopposed edge portions are heat-sealed on their inner sides, the throughcuts are distributed in the heat-sealed portions and in thenonheat-sealed portions falling outside the heat-sealed portions and thethrough cuts distributed in the heat-sealed portions are partly orwholly blocked with the heat seal layer and the through cuts distributedin the nonheat-sealed portions are not blocked with the heat seal layer.

When the easily openable tightly sealed bag is produced by inflictingthrough cuts in the substrate layer and superposing the heat seal layerthereon by the method of (2) and heat-sealing the opposed edge portionsto form a sealed part in the completed bag, the through cuts are partlyor wholly blocked with the heat seal layer and they are distributed onlyin the heat-sealed portions. In this case, when the inner sides of theedge portions are heat-sealed, the through cuts are distributed in theheat-sealed portions and in the nonheat-sealed portions alike and thesethrough cuts in both the heat-sealed portions and the nonheat-sealedportions are partly or wholly blocked with the heat seal layer.

Example 1 [Manufacture of device for imparting through cuts]:

FIG. 11 is a perspective view of protrusions 10 on a through cutimparting device of this invention in a magnified state. As illustratedin FIG. 12, cuts 21 are made in a flat, smooth metallic surface 20.Then, the surface portions separated from the metallic surface inconsequence of the work of making cuts 21 are raised substantiallyupright as indicated by the arrow of FIG. 12, and there are formed bluffsurfaces 12 as illustrated in FIG. 11. The bluff surfaces 12 have ontheir backs formed outer sloped surfaces 19 by the flat, smooth metallicsurface pulled up through the medium of ridge lines 22. By 11 aredenoted depressions which are formed on the flat, smooth metallicsurface by the insertion of the cuts. The angle which the bluff surfaces12 form relative to the flat, smooth metallic surface 20 is required toexceed 60° and desired to fall in the range of 80° to 100°. The metallicmaterial on which the protrusions of the shape described above areformed in a large number is hardened and used as a cutting blade of thisinvention.

Since the ridge lines 22 are formed by the cuts made in the metallicsurface, they are naturally sharp and constitute excellent cuttingedges. In the present working example, the protrusions 10 have a widthof 0.4 mm at their feet. As illustrated in FIG. 13, these protrusions 10are disposed in at least one row on the circumferential surface of aprocessing roll 13. FIG. 14 is a plan view illustrating the portion ofthe roll 13 indicated by a dash and dotted line in FIG. 13 in amagnified state. When this processing roll 13 is rotated and theprotrusions 10 are brought into pressed contact with the film, the ridgelines 22 function as cutting edges to inflict a linearly arranged groupof fine slender cuts in the film. Since the cutting edges are each inthe form of a mountain, the length of the cuts inflicted in the film canbe varied by regulating the pressure with which the cutting edges arepressed into the film. This device wears slowly and enjoys highdurability because the cutting blades have an appreciable thickness.

Example 2 [Manufacture of device]:

On the circumferential surface of a processing roll, a multiplicity ofcutting blades 23 each having a triangular cross section and possessinga cutting edge running parallel to the axis are disposed as illustratedin FIG. 16. Then, by cutting out the portions incicated by the brokenlines in FIG. 16, there are obtained protrusions 10 which retain part ofthe cutting edges 22 as illustrated in FIG. 17. The device so obtainedyields substantially the same results as the device of Example 1.

Example 3 [Production of easily openable tightly sealed bag]:

A composite laminated film of 720 mm in width and 74 μm in totalthickness consisting of the following structure was prepared by anextrusion laminating method:

    PET#.sub.12 /AC/LDPE.sub.15 /Al.sub.7 /IR.sub.40

wherein,

PET#₁₂ : biaxially stretched polyester film (E-5100 produced by ToyoboK. K.): 12 μm in thickness

AC:imine type anchor coat agent (WS-680 produced by Matsumoto Seiyaku K.K.): 0.01 g/m² of solid content

LDPE₁₅ : low-density polyethylene (Suntech LD, L-1850A produced by AsahiKasei Kogyo K. K.): 15 μm in thickness

Al₇ : flexible aluminum foil (produced by Tokai Kinzoku K. K.): 7 μm inthickness

IR₄₀ : ionomer (Himiran 1652 SR, produced by Mitsui-Du Pont PolychemicalK. K.): 40 μm in thickness

A group of cuts was inflicted in the above laminated film with thedevice of Example 1.

As illustrated in FIG. 15, the processing roll 13 and the retainer roll14 are held in mutual contact and are rotated in opposite directions atone equal peripheral speed. The film 8 is passed through the two rolls.During the course of this passage, the film 8 is pressed by theprotrusions 10 of the processing roll 13. This film 8 is fed from theroll 15. Consequently, through cuts are formed in three rows, two at adistance of 10 mm from the opposite edges of the film 8 and one at thecenter of the width of the film. Then, by cutting the film along thecentral array of through cuts, there are obtained two strips of filmeach measuring 350 mm in width.

As illustrated in FIG. 1, the portions of the obtained film which werecut into with the bluff surfaces of the device remained flat and theportions which received the insertion of the outer sloped surfaces weredeformed aslant downwardly, resulting in formation of the uneven filmsurfaces at the cut portions with the cuts therebetween. It was observedthat the opposite terminals of each through cut were cracked.

From the obtained film pillow type gusset bags each having the threeedge portions heat sealed and containing 250 g of instant coffee wereproduced by the use of an automatic bag making and bag-filling machine.

In the sealed part of each of the bags so produced by the automaticbag-making and bag-filling machine, the through cuts were wholly blockedwith the heat seal layer. When the opposed edge portions are heat-sealedby the automatic bag-making and bag-filling machine, they are sopositioned that the through cuts in one of the edge portions willdeviate from those in the other edge portion.

During the course of the production of bags, the transportation of theproduced bags, or the storage thereof, the film retained sufficientstrength without suffering any trouble. The bags consequently obtainedcould be opened with the force of finger tips at any desired point inthe longitudinal heat-sealed portions.

In this working example, the protrusions were arrayed orderly. Theprotrusions, if distributed irregularly, could be expected to bringabout the effect aimed at by this invention so long as they were formedwith sufficient density.

Example 4:

A composite laminated film of 770 mm in width and 70 μm in thicknessconsisting of the following structure was prepared by an extrusionlaminating process:

    ON#.sub.15 /AC/PE.sub.25 /EVA.sub.30

wherein,

ON#₁₅ :biaxially stretched 6-nylon film (Embrem produced by UNITIKA,Ltd.): 15 μm in thickness

AC:isocyanate type anchor coat agent (prepared by mixing EL-200 andCAT-200 both produced by Toyo Moton K. K. in the ratio of 13:1): 0.02g/m² of solid content

PE₂₅ :low-density polyethylene (Suntech LD, L-1850A produced by AsahiKasei Kogyo K. K.): 25 μm in thickness

EVA₃₀ : ethylene-vinyl acetate copolymer resin (Suntech EVA, EL-0990produced by Asahi Kasei Kogyo K. K.): 30 μm in thickness

The above isocyanate type anchor coat agent was applied to the biaxiallystretched 6-nylon film by a gravure coating method. The low-densitypolyethylene layer and the ethylene-vinyl acetate copolymer resin layerwere superposed to each other by a tandem extrusion laminating method.

A group of cuts was inflicted in the above laminated film with thedevice illustrated in FIG. 13 without giving rise to any waste scraps ofthe film.

The ethylene-vinyl acetate copolymer constituted the heat seal layer. Onthe circumferential surface of the processing roll 13, protrusions ofthe shape illustrated in FIG. 11 having the maximum width of 0.5 mm arearrayed in a total of four zigzag rows, two each at a center-to-centerdistance of 0.5 mm from the central zone of flat, smooth surface 1.5 mmin width left at the center of the width of the peripheral surface.Then, by following the procedure of Example 1, through cuts wereinflicted in the portions at a distance of 10 mm from the opposite edgesat an interval of 250 mm of width. Then, the film was cut in the centersof the arrayed groups of cuts to obtain the strips of film having awidth of 250 mm and containing groups of through cuts in the portions ata distance of not less than 0.75 mm from the opposite edges of the film.

As illustrated in FIG. 1, the portions of the obtained film which werecut into with the bluff surfaces of the device remained flat and theportions which received the insertion of the outer sloped surfaces weredeformed aslant downwardly, resulting in formation of the uneven filmsurfaces at the cut portions with the cuts therebetween. It was observedthat the opposite terminals of each through cut were cracked.

From the film so obtained, pillow type bags each having the edgeportions heat-sealed and containing 250 g of a piece of devil's-tonguejelly were produced by the use of an automatic bag-making andbag-filling machine. A micrograph illustrating the sealed portioncontaining cuts is shown in FIG. 22.

In each of the bags so produced by the automatic bag-making andbag-filling machine, the through cuts were partly blocked with the heatseal layer. During the heat sealing of the opposed edge portions withthe automatic bag-making bag-filling machine, these edge portions wereso positioned that the through cuts in one of the edge portions deviatedfrom those in the other edge portion.

During the course of the production of bags, the transportation of theproduced bags, or the storage thereof, the film retained sufficientstrength without suffering any trouble. The bags consequently obtainedcould be opened with the force of finger tips at any desired point inthe longitudinal heat-sealed portions.

Example 5:

A composite laminated film was prepared by following the procedure ofExample 4 except that through cuts were inflicted in the biaxiallystretched 6-nylon film with the device illustrated in FIG. 13immediately prior to laminating in the process of extrusion lamination.

Then, by following the procedure of Example 4, the laminated film wascut at the center of the groups of cuts, to afford two strips of filmhaving a width of 250 mm and containing through cuts in the portions ata distance of 0.75 mm inwardly from the oppositely edges of the film.The ethylene-vinyl acetate copolymer constituted the heat seal layer.

From the film so obtained, pillow type bags each having the edgeportions heat-sealed and containing 250 g of a piece of devil's-tonguejelly were produced by the use of an automatic bag-making andbag-filling machine.

By visual inspection, the cuts in the tightly sealed bag produced by theautomatic bag-making and bag-filling machine were found to be whollyblocked with the heat seal layer.

During the course of the production of bags, the transportation of theproduced bags, or the storage thereof, the film retained sufficientstrength without suffering any trouble. The bags consequently obtainedcould be opened with the force of finger tips at any desired position inthe longitudinal heat-sealed portions.

Example 6:

A composite laminated film consisting of a stretched nylon film (15 μmin thickness) coated with vinylidene chloride resin as a substrate layerand a linear low-density polyethylene (25 μm in thickness) as a heatseal layer and measuring 820 mm in width and 40 μm in total thicknesswas used to produce vacuum-packed bags for domestic use with abag-making machine capable of sealing three sides.

The laminated film used in this Example had the following structure indetail:

    KON#.sub.15 /adhesive/L-LDPE.sub.25

wherein,

KON#₁₅ :polyvinylidene chloride-coated biaxially stretched 6-nylon(Hahden film, KN 8002 produced by Toyobo K. K.): 17 μm in thickness

Adhesive:isocyanate type adhesive (prepared by mixing AD-335AT andCAT-10 both produced by Toyo Moton K. K. in the ratio of 100:6): 2 μm inthickness (2-3 g/m² of solid content)

L-LDPE₂₅ :linear low-density polyethylene (Tocello TUX-FC produced byTokyo Cellophane K. K.): 25 μm in thickness

The polyvinylidene chloride coat surface of the above polyvinylidenechloride coated biaxially stretched 6-nylon was coated with theisocyanate type adhesive by a gravure coater. The linear low-densitypolyethylene layer had its one surface subjected to corona dischargetreatment. This treated surface was applied to the aboveadhesive-applied surface. Then, the above plies were subjected to a drylaminating method to produce a composite film.

In the process of forming the bags, the film taken out of the source ofsupply was folded in half and a group of through cuts was inflicted withthe device illustrated in FIG. 13 in the portions which constitute thelongitudinal sealed portions and the end portions of the bags to bemade. Then, the film was heat-sealed to obtain the bags of 200 mm inwidth and 300 mm in length whose three end portions had been sealed.

Through cuts were formed in one end portion of the film folded into two(410 mm in width), in a portion at a distance of 200 mm inwards from theaforesaid end portion, and in a portion at a distance of 10 mm inwardsfrom the other end portion. The remaining margin of 10 mm was cut off.

The bags thus produced had their two longitudinal end portions and onelateral end portion heat-sealed, and the top end was not sealed. The twolongitudinal heat-sealed end portions contained a group of cuts in thewidth of about 2 mm to the whole longitudinal length of the bags. Allthe cuts had been covered with the heat seal layer.

During the course of the transportation of the produced bags, thestorage thereof, or the handling in filling the bag in a house, the bagcaused no trouble. The bag could be opened with the force of finger tipsat any desired point in the longitudinal sealed portions.

What is claimed is:
 1. An easily tearing openable tightly sealed plasticbag formed of a film containing at least a substrate layer and a heatseal layer, said bag having a sealed part which is comprised of at leasttwo substrate layers held fast to an adjacent heat seal layer, so thatthe heat seal layer is disposed between the substrate layers forming asealed edge line proximate to a border end of the substrate layers,which bag is characterized by said sealed part containing in thesubstrate layers thereof a multiplicity of through cuts, substantiallyformed over a major portion of the sealed edge line and disposed atangles in the range of 70° to 110° relative to the sealed edge line, atleast a significant amount of said through cuts being wholly orpartially filled by the heat seal layer in such a manner that the heatseal layer penetrates into the through cuts and closes said throughcuts; the tensile strength of the heat seal layer being smaller thanthat of the substrate layer and the tear strength of the heat seal layerbeing greater than that of the substrate layer.
 2. An easily openabletightly sealed plastic bag according to claim 1, wherein said throughcuts are slender slits inserted substantially perpendicularly to theedges of said bag.
 3. An easily openable tightly sealed plastic bagaccording to claim 2, wherein said through cuts formed in the substratelayer of one of two heat-sealed plies of film in said sealed part aredeviated from those formed in the substrate layer of the otherheat-sealed ply of film.
 4. An easily openable tightly sealed plasticbag according to claim 2, wherein said through cuts formed in thesubstrate layer of one of two heat-sealed plies of film in said sealedpart are superposed on those formed in the substrate layer of the otherheat-sealed ply of film.
 5. An easily openable tightly sealed plasticbag according to claim 2;wherein the tensile strength of the heat seallayer material is not more than 2/3 and not less than 1/20 of thetensile strength of the substrate layer.
 6. An easily openable tightlysealed plastic bag according to claim 1;wherein the tear strength of theheat sealed layer is not less than five times and not more than onehundred and fifty times that of the substrate material.
 7. An easilyopenable tightly sealed plastic bag according to claim 1;wherein thethickness ratio of the substrate layer to the heat seal layer fallswithin the range of 5:1 to 1:10.
 8. An easily openable tightly sealedplastic bag according to claim 2;wherein the thickness of the heat seallayer is 10 to 100 μm.
 9. An easily openable tightly sealed plastic bagaccording to claim 1;wherein the thickness of the substrate layer is 10to 50 μm.